Add the ability to amplify metric payloads

It may be helpful, for load testing, for one node to be able to send
extra metrics, multiples of its typical payload.  One node could thus
impersonate two or three or ten in terms of the total number of metrics
submitted.

This patch adds this ability through use of an 'amplifier'
configuration option.  If set above zero, each measurement will be
duplicated, with an additional 'amplifier' dimension, making it a
unique metric.  The higher 'amplifier' configuration value is raised,
the more multiples of each metric will be submitted.

To configure, run monasca-setup with the --amplifier parameter, as in
'--amplifier 2' for two additional sets of metrics per API payload.

Change-Id: Ibc277bb31bca449510fc7bb6d5520b329a78aea4
Agent documentation updates

Add monasca-setup's new 'amplifier' parameter to the README, and fix
a few minor spacing issues in monasca-setup's --help output.

Change-Id: I5b7a0399ed7b15e7f0a302cf42e200fe080efb70
Merge commit 'c0a5019b438a2ef7a859e8cfdce332f39edf176c'