pmbootstrap.py: move all features to pmb:main()

Prepare to modernize the python packaging. pmbootstrap.py will not be
part of the packaging, so add a note there and move both features
(python version check, ^C check) to pmb/__init__.py:main().

Reviewed-by: Luca Weiss <luca@z3ntu.xyz>
Link: https://lists.sr.ht/~postmarketos/pmbootstrap-devel/%3C20230407233026.1712-3-ollieparanoid@postmarketos.org%3E

pmb/__init__.py

@@ -14,6 +14,13 @@ from .helpers import logging as pmb_logging
 from .helpers import mount
 from .helpers import other
 
+version = sys.version_info
+if version < (3, 7):
+    print("You need at least Python 3.7 to run pmbootstrap")
+    print("(You are running it with Python " + str(version.major) +
+          "." + str(version.minor) + ")")
+    sys.exit()
+
 
 def main():
     # Wrap everything to display nice error messages
@@ -59,6 +66,10 @@ def main():
                          " shutdown' as necessary)")
         logging.info("DONE!")
 
+    except KeyboardInterrupt:
+        print("\nCaught KeyboardInterrupt, exiting …")
+        sys.exit(130)  # SIGINT(2) + 128
+
     except Exception as e:
         # Dump log to stdout when args (and therefore logging) init failed
         if not args:

pmbootstrap.py

@@ -4,17 +4,9 @@
 # SPDX-License-Identifier: GPL-3.0-or-later
 # PYTHON_ARGCOMPLETE_OK
 import sys
-version = sys.version_info
-if version < (3, 7):
-    print("You need at least Python 3.7 to run pmbootstrap")
-    print("(You are running it with Python " + str(version.major) +
-          "." + str(version.minor) + ")")
-    sys.exit()
 import pmb
 
+# A convenience wrapper for running pmbootstrap from the git repository. This
+# script is not part of the python packaging, so don't add more logic here!
 if __name__ == "__main__":
-    try:
-        sys.exit(pmb.main())
-    except KeyboardInterrupt:
-        print("\nCaught KeyboardInterrupt, exiting …")
-        sys.exit(130)  # SIGINT(2) + 128
+    sys.exit(pmb.main())