mount: cache blkid information
mount: cache blkid information

During the mount of a device a call to blkid is done, to get
information of the current devices.

blkid is a slow operation, to avoid that use an internal cache,
that is specified in /etc/blkid configuration file, but a single
blkid can still redo this cache file, making the second call
equally slow.

This patch cache the blkid information for _active_mountinfo in
the __context__ dict, making the next mount action a fast
operation.

(cherry picked from commit c1ede1d97c2c4f4cf7ae7ca84fe19f6bbcaa27cb)

saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt