No longer any need to pass admin context to aggregate DB API methods

No longer need to pass an elevated context because the check of
admin has been removed in following patch:
https://review.openstack.org/67026

This patch removes the admin context elevated
method in nova/scheduler sub-folder since it's not required any more.

Change-Id: Ib768c97c9e84a9db44d866fa5fbfc4665ad7c73e
Partial-Bug: #1279216
Rename quota_injected_file_path_bytes

Rename quota_injected_file_path_bytes to
quota_injected_file_path_length, and change help message to
'Length of injected file path'.

DocImpact

Change-Id: Id6b9c03b37664601937e4bc9d4a8d8026c4d3b63
Closes-bug: 1258175
Merge "Rename quota_injected_file_path_bytes"
Merge "No longer any need to pass admin context to aggregate DB API methods"