Fix typos in code comments & docstrings

Conflicts:
	ceilometer/storage/mongo/utils.py

Change-Id: Ia5937026018bb5441b7a5b6d82ce074889dfe78b
Fix call to meter-list in measurements doc

-s is not an accepted argument.

Change-Id: I42567cf9187bb70665abfa335a8dcdefcc05c9fe
Closes-Bug: 1340775
Fix incorrect use of timestamp in test

The timestamp used has a very slim chance of being in
a different second than actually desired which would
tickle the bug. The bug itself is simply that the
mapping between sample and timestamp was incorrect.

To make sure that there isn't confusion over distinct
timestamps, _make_timestamps has been changed so that
if multiple timestamps are requested, each is a second
after the previous.

Change-Id: I22d999c506a30d4ca6b8dd7e9de501570257b99e
Closes-bug: 1341142
Improves pipeline transformer documentation

Adds the Transformers section in the configuration documentation.
Describes each transformer's function, parameters and provides
an example.

Change-Id: I8f2218edcdd23fbd42a160afc5cc8e0af8d73af7
Merge "Fix call to meter-list in measurements doc"
Merge "Improves pipeline transformer documentation"
Use hmac.compare_digest to compare signature

hmac.compare_digest must be used to compare sample
signature to avoid timing-attack.

We also provide a best-effort version of hmac.compare_digest
for python version that doesn't have the C version.

Closes bug #1332390

Change-Id: Ia313c98b7cccf0e8aed4fb933292bd7e6141b801
Merge "Fix typos in code comments & docstrings"
Merge "Fix incorrect use of timestamp in test"