misc: Allow to cross-execute the tests using qemu

When cross-compiling osmo-bts/osmo-pcu one can not easily
execute the testsuite. By adding the OSMO_QEMU variable in
front of the normal execution we can execute the tests. This
should work for native and cross builds.

$ OSMO_QEMU="qemu-arm -L /opt/poky/1.1.2/sysroots/armv5te-poky-linux-gnueabi/" make check
1 file changed