oeqa/sdk: add helpers to check for and install packages

oeqa/sdk: add helpers to check for and install packages

The existing tests simply look at the manifest to determine if a test
should be ran or not based on dependencies. Whilst this works for
Traditional SDKs, it fails for Extensible SDKs if they've been built in
minimal mode, where the manifest will be empty.  However, minimal eSDKs
might well have available sstate to install the missing dependencies.

Add a pair of helper functions to ensure that a package is available, or
skip the test.  This handles nativesdk- vs -native (SDK vs eSDK) and
will try to sdk-install missing dependencies into an eSDK if they're not
already installed.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>