erofs: Make smaller lzma erofs images by default

After some experimentation these seem to be reasonable defaults:

mkfs.erofs -z lzma -Ededupe,all-fragments -C 131072 --all-time ...

Higher compression levels above the default of 6 don't make smaller
images. The dedupe and all-fragment options, while they make it run
slower, result in a smaller image size (about 75MB smaller), and
--all-time reduces it by about another megabyte.

These can always be overridden by creating a config file like this:

[compression.erofs]
type = lzma
args = -C 131072

and passing it to lorax with the '--config PATH' argument.

Related: RHEL-48606

src/pylorax/__init__.py

@@ -117,7 +117,7 @@ def configure(self, conf_file="/etc/lorax/lorax.conf"):
 
         self.conf.add_section("compression.erofs")
         self.conf.set("compression.erofs", "type", "lzma")
-        self.conf.set("compression.erofs", "args", "-E dedupe,all-fragments")
+        self.conf.set("compression.erofs", "args", "-E dedupe,all-fragments -C 131072 --all-time")
 
         # read the config file
         if os.path.isfile(conf_file):