After commit b3f1c8c4 "qemu-pr-helper: use new
libmultipath API", QEMU started using new libmultipath API, which is not
available on CentOS 7.x.

This fixes that by probing the new libmultipath API in configure.  If it fails,
then try probing the old API.  If it fails, then consider libmultipath not
available.

With this, configure script defines CONFIG_MPATH_NEW_API that is used in
scsi/qemu-pr-helper.c to use the new libmultipath API.

Fixes: b3f1c8c4
BugLink: https://bugs.launchpad.net/qemu/+bug/1786343Signed-off-by: NMurilo Opsfelder Araujo <muriloo@linux.ibm.com>
Message-Id: <20180810141116.24016-1-muriloo@linux.ibm.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>