runqemu: don't complain about conflicting machines if they are equal

runqemu: don't complain about conflicting machines if they are equal

When the MACHINE variable was set as an environment variable, via
"export MACHINE=qemuarm" and runqemu was executed as "runqemu qemuarm"

The confusing error message appears:
Error: conflicting MACHINE types [qemuarm] and [qemuarm]

This checks if the two values are equal, in that case there is no problem
and execution can continue.

Signed-off-by: Pascal Bach <pascal.bach@siemens.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>