resource-agents: Fix for reading /proc/mounts in fs-lib.sh

This patch fixes a problem with the fs resource agent
that caused status checks to mistakenly fail as a result
of /proc/mounts changing while it was being read.

Original patch from John Ruemker <jruemker@redhat.com>

Resolves rhbz#853249

Signed-off-by: Ryan McCabe <rmccabe@redhat.com>