Move non-AB OTA generation code to a separate file

Test: Generate a non-AB OTA, apply it
Change-Id: I2f1afbe70d17356fcbf4d59901d201a76a3d6c4f
diff --git a/tools/releasetools/common.py b/tools/releasetools/common.py
index 1846a67..89900d3 100644
--- a/tools/releasetools/common.py
+++ b/tools/releasetools/common.py
@@ -1227,7 +1227,7 @@
     cmd = ["mkbootfs", os.path.join(sourcedir, "RAMDISK")]
   p1 = Run(cmd, stdout=subprocess.PIPE)
   if lz4_ramdisks:
-    p2 = Run(["lz4", "-l", "-12" , "--favor-decSpeed"], stdin=p1.stdout,
+    p2 = Run(["lz4", "-l", "-12", "--favor-decSpeed"], stdin=p1.stdout,
              stdout=ramdisk_img.file.fileno())
   else:
     p2 = Run(["minigzip"], stdin=p1.stdout, stdout=ramdisk_img.file.fileno())