libct/checkProcMounts: optimize
libct/checkProcMounts: optimize

Commit 9c1242ecb ("Add white list for bind mount chec", Jan 6 2016)
added a set of entries under /proc which we allow to be mounted to,
for the benefit of lxcfs-like fuse-backed hack to have container's
own version of /proc/meminfo etc.

For some reason, the allow list check is performed at the very
beginning of the function, which is not optimal.

Move the check to the end -- at this point in the code we already
know we're under /proc, so it make sense to consult the allow list.

This makes the code slightly more logical and hopefully slightly faster.

Signed-off-by: Kir Kolyshkin <3a017b8ddb3f9cf3e4a59978b004111bdeb97f08@gmail.com>

opencontainers/runc,estesp/runc,estesp/runc,dqminh/runc,kolyshkin/runc,kolyshkin/runc,opencontainers/runc,dqminh/runc,dqminh/runc,rhatdan/runc,rhatdan/runc,kolyshkin/runc,opencontainers/runc,rhatdan/runc,kolyshkin/runc,opencontainers/runc,dqminh/runc,estesp/runc,rhatdan/runc