Increases the number of processes in CentOS 6.X

Increases the number of processes per user in /etc/security/limits.d/90-nproc.conf
for CentOS 6.X due to bug https://bugzilla.redhat.com/show_bug.cgi?id=919793

Change-Id: I76f258f33325f80fe06167dec08d81dabd292163
Closes-Bug: 1376564
Merge "Increases the number of processes in CentOS 6.X"