The function guru_meditation_report() currently uses the User-defined
signal SIGUSR1 to kill a Nova Compute process so that a Guru Meditation
Report is generated.

Testing locally, in a DevStack instance, manually attempting to kill a
Nova compute process [kill -s USR1 `pgrep nova-compute`] does not result
in process being terminated, and no error report generated.

It turns out[1] that SIGUSR1 is used by Apache 'mod_wsgi'.

Using the signal SIGUSR2 resolves this issue (i.e. 'nova-compute'
process is terminated, and the Guru Meditation Report is generated).

So, use USR2, instead of USR1.

Corresponding oslo.reports related commit[2].

[1] https://code.google.com/p/modwsgi/wiki/ConfigurationDirectives#WSGIRestrictSignal
[2] 45b1c02d113051d147e54ef921ce8e94135542d8 -- guru_meditation_report:
Use SIGUSR2 instead of SIGUSR1
[3] Original DevStack commit that brought in this change --
2ebe993b25462919e8aeeb896c9f91b6be7aa573

Change-Id: I8a7eaf71b83edca3c80074d6bf2d471e3db6142b