Signed-off-by: NAshwin Agrawal <aagrawal@pivotal.io>

Using gp_segment_configuration catalog table easily can find if mirrors exist or
not, do not need special table to communicate the same. Earlier
gp_fault_strategy used to convey 'n' for mirrorless system, 'f' for replication
and 's' for san mirrors. Since support for 's' was removed in 5.0 only purpose
gp_fault_strategy served was mirrored or not mirrored system. Hence deleting the
gp_fault_strategy table and at required places using gp_segment_configuration to
find the required info.

This bumps the copyright years to the appropriate years after not
having been updated for some time.  Also reformats existing code
headers to match the upstream style to ensure consistency.

Current FTS probe relies on file replication data structures mostly
found in pmModuleState.  This commit establishes an empty FTS probe
response packet that primaries using segment WAL replication can fill
out later.

We also introduce the 'w' fault_strategy (WAL replication) to replace
the 'f' fault_strategy (file replication).

This commit is carved and modified from a previously closed PR:
https://github.com/greenplum-db/gpdb/pull/2936

Authors: Abhijit Subramanya and Jimmy Yih

An FTS probe to the primaries in a mirrorless cluster will never
result in the update of gp_segment_configuration.  If a primary goes
down, we must keep the primary marked as up so that gpstart can start
the primary back up.  All transactions will abort and nothing should
work except for read-only queries to master-only catalog tables.

Stopping the FTS probes for mirrorless cluster introduced an infinite
loop in FtsNotifyProber in which the dispatcher waits in an infinite
loop for fts_statusVersion to change.  To break the infinite loop, we
acknowledge the forced probe request as a no-op and update
fts_statusVersion to break the loop for the dispatcher.  The
dispatcher should then act same as before this commit.

We also add #define for character value of GpFaultStrategy.

Authors: Xin Zhang, Ashwin Agrawal, and Jimmy Yih

The whole cdb directory was shipped to end users and all header files
that cdb*.h included are also need to be shipped to make checkinc.py
pass. However, exposing gp_libpq_fe/*.h will confuse customer because
they are almost the same as libpq/*, as Heikki's suggestion, we should
keep gp_libpq_fe/* unchanged. So to make system work, we include
gp-libpg-fe.h and gp-libpq-int.h directly in c files that need them

The SAN FTS failover strategy is deprecated and no longer maintained,
as it's no longer needed. Retire the dead code to clean up. Since we
currently are in catalog freeze, the gp_san_configuration catalog is
left in place but will be removed once we open up for the next major
version cycle. Since the gp_san_config header file contains catalogs
for general FTS fault strategies, rename the file for clarity.

FTS processes uses SnapshotNow everywhere to perform catalog lookups, but
certain other interfaces like heap_hot_search_buffer are coded with assumption
that transaction always takes an snapshot. Hence to fulfill the same added to
take snapshot after starting transaction in FTS.

This removes all the code for inserting, updating, or deleting through
CaQL context. All the code surrounding the updates are also converted to
use regular SysCache lookups or systable scans.

Note that this leaves the support for deleting rows with
caql_getcount("DELETE ...") alone. For now. This commit is all about
removing the functions that modify the current row of a caql scan.

FTS doesn't actually seem to use the superuser's username for anything.
That allowed removing probeUser and retrieveUserAndDb(). All the remaining
calls to FtsFindSuperuser() were from cdbresynchronizechangetracking.c,
but all of those callers just discarded the return value.
FtsFindSuperuser() doesn't throw any errors, either, so it didn't serve
any error-checking purpose either. Remove it all.