Memcache connection pool excess check

When memcache pool depletes exceeding connections are created.
Then they are pushed back the to pool via a blocking operation ``put``.
As a result thread, attempting to release connection, blocks.

This patch adds a check preventing pushung the excess back to the pool,
closing released connection instead.

Change-Id: I17756fb5f27cb6a950c647590e2a9e0a83c336ca
Closes-Bug: #1401108
Closes-Bug: #1400326
Merge "Memcache connection pool excess check"