make xz options configurable

Fixes: https://pagure.io/koji/issue/1901

builder/kojid

@@ -4093,7 +4093,7 @@ class BaseImageTask(OzImageTask):
                               'xz-cp-%s-%s.log' % (format, self.arch))
         log_output(self.session, cmd[0], cmd, conlog, self.getUploadDir(),
                    logerror=1)
-        cmd = ['/usr/bin/xz', '-z9T2', rawimg]
+        cmd = ['/usr/bin/xz', self.options.xz_options, rawimg]
         conlog = os.path.join(self.workdir,
                               'xz-%s-%s.log' % (format, self.arch))
         log_output(self.session, cmd[0], cmd, conlog, self.getUploadDir(),
@@ -6371,6 +6371,7 @@ def get_options():
                 'failed_buildroot_lifetime': 3600 * 4,
                 'rpmbuild_timeout': 3600 * 24,
                 'oz_install_timeout': 0,
+                'xz_options': '-z6T0',
                 'task_avail_delay': 300,
                 'cert': None,
                 'ca': '',  # FIXME: Unused, remove in next major release

builder/kojid.conf

@@ -116,6 +116,9 @@ from_addr=Koji Build System <buildsys@example.com>
 ;if set to True, failing subtask will not automatically cancel other siblings
 ;build_arch_can_fail = False
 
+;image build with raw-xz type will use following xz options
+;xz_options=-z6T0
+
 ;if set to True additional logs with timestamps will get created and uploaded
 ;to hub. It could be useful for debugging purposes, but creates twice as many
 ;log files

docs/source/kojid_conf.rst

@@ -170,6 +170,11 @@ Building
       This value is used for waiting on all xmlrpc calls to hub. By default
       there is no timeout set.
 
+   xz_options=-z6T0
+      Image builds with ``raw-xz`` type will use this setting when compressing
+      the image. Default value is compromise between speed and resource usage.
+      Only one option (not space-separated) is allowed here for now.
+
 RPM Builds
 ^^^^^^^^^^
 .. glossary::