package_{ipk, deb, rpm}.bbclass: support additional user-defined metadata

package_{ipk, deb, rpm}.bbclass: support additional user-defined metadata

Additional metadata from user-defined variable is written into
control/spec file of binary package.

Three variables are searched for adiitional package metadata:

  * PACKAGE_ADD_METADATA_<PKGTYPE>_<PN>
  * PACKAGE_ADD_METADATA_<PKGTYPE>
  * PACKAGE_ADD_METADATA

First found variable with defined value wins.

<PN> is a package name. <PKGTYPE> is a distinct name of specific
package type:

  * IPK for .ipk packages
  * DEB for .deb packages
  * RPM for .rpm packages

Variable can contain multiple [one-line] metadata fields separated by
literal sequence '\n'. Separator can be redefined through variable flag
'separator'. In package control/spec file separator is replaced by
newline character.

(From OE-Core rev: 773d7352309241e15ef5acadcbe416bdd7d45c18)

Signed-off-by: Leonid Borisenko <ive.found@gmail.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>