Suppress PETSc's unused options warning when Problem/solve=false

[pbehne]

Motivation

Users can choose to run an MOOSE input without solving by setting Problem/solve=false. When this is done, however, PETSc sees options that are used during the solve as 'unused', and emits a warning. Since the user intentionally instructs MOOSE not to solve, these warnings are irrelevant and should not be displayed to the user.

Design

One possible design is to set PETSc's 'options_left' parameter to false when Problem/solve=false. This will suppress the warning.

Impact

Less annoying warnings to the user.

[pbehne]

@joshuahansel