3118 petsc options warning

[tomc271]

Set option options_left to 0 when initialising PETSc.
Fixes #3118

[bendudson]

Does this mean PETSc would no longer warn if PETSc options were mis-typed?

Another way to fix #3118 might be to not pass argc/argv to PETSc. We already have options that get passed through to PETSc, that we can set in the BOUT.inp file or command line e.g.

petsc:ksp_monitor=true

is the same as passing

-ksp_monitor

This would avoid having to separate BOUT++ from PETSc options in argv.

[tomc271]

This (not passing argc/argv to PETSc) sounds like a better approach.
I'll close this PR and open a new one for that.