devtools: add verbose option to meson build test

devtools: add verbose option to meson build test

When running ninja, the commands are, by default, always printed on top of
each other. For those who want more detail in the output, two levels of
verbose output has been added to the test-meson-builds script. When "-v" is
passed, or the "TEST_MESON_BUILD_VERBOSE" flag is set in the environment,
then the output of ninja is passed through "cat" to prevent each line
overwriting the next. If "-vv" is passed, or
"TEST_MESON_BUILD_VERY_VERBOSE" is set in the environment, then ninja is
called with the "-v" flag to print out each command in full as it is
executing.

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>