Add option to make probetests more brittle

Currently probetests take advantage of a number of assumptions about the SUT.
Unfortunately after some time with a working SAIO, configuration drift may
result in a system that is no longer compatible with these assumptions.  To
help weary developers more quickly identify the changes they've made since
they last ran probetests successfully, some handy validators have been added
to test.probe.common

Additionally a new option 'validate_rsync' in test.conf, when enabled, will
run a series of up front validations during the setup of each probetest by
inspecting the ring, the mounted devices, and the rsync exports ("modules") in
order to ensure that when probetests fail the do so early and with specific
complaints.

To preserve existing failures, the option is disabled by default.

Change-Id: I2be11c7e67ccd0bc0589c360c170049b6288c152
Obscure the X-Auth-Token in proxy log

The X-Auth-Token is sensitive data. If revealed to an unauthozied person,
they can now make requests against an account until the token expires.

This implementation maintains current behavior (i.e, the token
is logged). Implementers can choose to set reveal_sensitive_prefix
to (e.g.) 12 so only first 12 characters of the token are logged.
Or, set to 0 to replace the token with "...".

DocImpact

Part of bug #1004114

Change-Id: Iecefa843d8f9ef59b9dcf0860e7a4d0e186a6cb5
Merge "Obscure the X-Auth-Token in proxy log"
Merge "Add option to make probetests more brittle"