package_manager.py: Move opkg_query() outside of Indexer class

package_manager.py: Move opkg_query() outside of Indexer class

When using the opkg and apt-get package managers the function
opkg_query() can be useful when query for package information.

This change moves the function outside the Indexer class so
the Indexer, OpkgPM, DpkgPM can benefit from it.

[YOCTO #9569]

Signed-off-by: Mariano Lopez <mariano.lopez@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>