client: quit on failed remount during dentry invalidate test

client: quit on failed remount during dentry invalidate test

Fixes: http://tracker.ceph.com/issues/22269
Signed-off-by: Patrick Donnelly <pdonnell@redhat.com>
(cherry picked from commit 5b2b1d14468c290c56ee6c95ea557c99464e0098)

Conflicts:
	PendingReleaseNotes - put the release note under 10.2.11
	src/ceph_fuse.cc - changed order of client_try_dentry_invalidate and
	    can_invalidate_dentries assignments to match master, and use jewel
            form of g_conf for accessing config option values
	src/client/Client.cc - code being replaced by _do_remount() calls is
	    different in jewel, and use jewel convention for accessing config
            option values
	src/common/legacy_config_opts.h - file does not exist in jewel
	src/common/options.cc - file does not exit in jewel; made the changes
            manually in src/common/config_opts.h