Add how to update a default quota value for Compute.

Partial-Bug: #1195571

Also, Admin User and Compute Admin guides basically
need the same quota info. So split out Compute and
Block Storage-specific info from the
section_cli_set_quotas.xml file so that they can be
separately referenced. section_cli_set_quotas.xml
and section_compute-configure-quotas.xml file now
reference new xml files.

Change-Id: I56410fe308d05a3e8b7381423e2e6adc25cca9c9
Merge "Add how to update a default quota value for Compute."