skippkg-finder: move extra packages to the OSRT attribute

The extra packages are packages should be skipped in ftp-tree but we
won't for some reasons, packagelist is not fixed depend on package
status in SLE side, move the list to OSRT attribute avoiding modify this
list so often.

skippkg-finder.py

@@ -17,6 +17,7 @@ from osc.core import makeurl
 from osc import oscerr
 import osclib
 from osclib.core import source_file_ensure
+from osclib.conf import Config
 
 SUPPORTED_ARCHS = ['x86_64', 'i586', 'aarch64', 'ppc64le', 's390x']
 DEFAULT_REPOSITORY = 'standard'
@@ -32,6 +33,12 @@ class SkippkgFinder(object):
         self.apiurl = osc.conf.config['apiurl']
         self.debug = osc.conf.config['debug']
 
+        config = Config.get(self.apiurl, self.opensuse_project)
+        # binary rpms of packages from `skippkg-finder-skiplist-ignores`
+        # be found in the `package_binaries` thus format must to be like
+        # SUSE:SLE-15:Update_libcdio.12032, PROJECT-NAME_PACKAGE-NAME
+        self.skiplist_ignored = set(config.get('skippkg-finder-skiplist-ignores', '').split(' '))
+
     def is_sle_specific(self, package):
         """
         Return True if package is provided for SLE only or a SLE forking.
@@ -274,30 +281,7 @@ class SkippkgFinder(object):
         # eg. SUSE:SLE-15-SP3:GA has qpdf/libqpdf28 but cups-filter was build
         # in/when SLE15 SP2 which requiring qpdf/libqpdf6, therefore old
         # qpdf/libqpdf6 from SLE15 SP2 should not to be missed.
-        extra_packagelist = [
-                # gnome-software requirement
-                'SUSE:SLE-15-SP2:Update_libxmlb.15999',
-                # cups-filter requirement
-                'SUSE:SLE-15-SP2:GA_qpdf',
-                # libcdio_paranoia2 requirement
-                'SUSE:SLE-15:Update_libcdio.12032',
-                # libstoken1 requirement
-                'SUSE:SLE-15:Update_libnettle.19992',
-                # python2-Pillow requirement
-                'SUSE:SLE-15:Update_libwebp.19719',
-                # amarok requirement
-                'SUSE:SLE-15:Update_mariadb.20531',
-                # bogofilter requirement
-                'SUSE:SLE-15:GA_gsl',
-                # gnome-builder requirement
-                'SUSE:SLE-15-SP2:GA_vala',
-                # hfst-ospell requirement
-                'SUSE:SLE-15:Update_icu.14528',
-                # for zypper dup reason
-                'SUSE:SLE-15-SP2:Update_icu.18168',
-                'SUSE:SLE-15-SP2:Update_gnome-desktop.16620',
-                ]
-        for pkg in extra_packagelist:
+        for pkg in self.skiplist_ignored:
             selected_binarylist += package_binaries[pkg]
 
         # Preparing a packagelist for the skipping candidate