common-utils: new dirent compatible time fmt

Introduce a new time format without "/" and spaces, in order to
be used in (virtual) filenames.

Change-Id: I468be54f1ec7f45265add4c458e19d95567439f7
BUG: 1089216
Signed-off-by: Anand Avati <avati@redhat.com>
Reviewed-on: http://review.gluster.org/7507
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Pranith Kumar Karampuri <pkarampu@redhat.com>