oeqa/utils/commands.py: allow use of binaries from native sysroot

oeqa/utils/commands.py: allow use of binaries from native sysroot

Tests may need to run a native tool that is not available on the host
filesystem, but can be built using one of the *-native recipes. In such case,
the tool will be available in native sysroot, and running in from that location
will require adjustments to PATH.

runCmd() can now take a path to native sysroot as one of its arguments and
setup PATH accordingly.

(From OE-Core rev: f2a04631949db72d4261d1c142c5044fad3741f9)

Signed-off-by: Maciej Borzecki <maciej.borzecki@rndity.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>