Add .gitignore for tests/

The new autotests in tests/ generate a number of files, both
executable and source, which are not caught by the existing .gitignore
files.  This patch adds a new .gitignore in tests/ which covers these.

[Changed 'rtc-test' to '*-test' so future tests do not need to be added
to .gitignore on a case-by-case basis.  Stefan]
Signed-off-by: NDavid Gibson <david@gibson.dropbear.id.au>
Signed-off-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>

tests/.gitignore

+check-qdict
+check-qfloat
+check-qint
+check-qjson
+check-qlist
+check-qstring
+test-qapi-types.[ch]
+test-qapi-visit.[ch]
+test-qmp-commands.h
+test-qmp-commands
+test-qmp-input-strict
+test-qmp-marshal.c
+*-test