Fallback to the regular .zip container support if apktool is not available by...

Fallback to the regular .zip container support if apktool is not available by simply swapping out the container class at import-time. (Re: #86)

Alternative solution pending.

diffoscope/comparators/apk.py

@@ -22,7 +22,7 @@ import os.path
 import logging
 import subprocess
 
-from diffoscope.tools import tool_required
+from diffoscope.tools import tool_required, find_executable
 from diffoscope.tempfiles import get_temporary_directory
 
 from .utils.file import File
@@ -172,7 +172,9 @@ class ApkFile(File):
     FILE_TYPE_HEADER_PREFIX = b"PK\x03\x04"
     FILE_TYPE_RE = re.compile(r'^(Java|Zip) archive data.*\b')
     FILE_EXTENSION_SUFFIX = '.apk'
-    CONTAINER_CLASS = ApkContainer
+    CONTAINER_CLASS = (
+        ApkContainer if find_executable('apktool') else ZipContainer
+    )
 
     def compare_details(self, other, source=None):
         return zipinfo_differences(self, other)