releasetools: Make apex_utils Python 3 compatible.

In order to get a Python 2 and 3 compatible re-raise behavior, this CL
removes the stack traceback for the lines within apex_util module (i.e.
sys.exc_info()[2]). It's not a big loss in practice, since we only have
one line within the try-except block (`common.RunAndCheckOutput()`)
that's no longer reported in the traceback.

Using `six` module could better solve this, but only after building
releasetools as python_binary_host modules where we can properly handle
the module dependency.

Bug: 131631303
Test: TreeHugger
Test: `python -m unittest test_apex_utils`
Test: `python3 -m unittest test_apex_utils`
Change-Id: I0c5a72ec9fad5ff9d8c9c94d29e813e433ec2921

tools/releasetools/apex_utils.py

@@ -59,9 +59,9 @@ def SignApexPayload(payload_file, payload_key_path, payload_key_name, algorithm,
   try:
     common.RunAndCheckOutput(cmd)
   except common.ExternalError as e:
-    raise ApexSigningError, \
+    raise ApexSigningError(
         'Failed to sign APEX payload {} with {}:\n{}'.format(
-            payload_file, payload_key_path, e), sys.exc_info()[2]
+            payload_file, payload_key_path, e))
 
   # Verify the signed payload image with specified public key.
   logger.info('Verifying %s', payload_file)
@@ -75,9 +75,9 @@ def VerifyApexPayload(payload_file, payload_key):
   try:
     common.RunAndCheckOutput(cmd)
   except common.ExternalError as e:
-    raise ApexSigningError, \
+    raise ApexSigningError(
         'Failed to validate payload signing for {} with {}:\n{}'.format(
-            payload_file, payload_key, e), sys.exc_info()[2]
+            payload_file, payload_key, e))
 
 
 def ParseApexPayloadInfo(payload_path):
@@ -100,9 +100,9 @@ def ParseApexPayloadInfo(payload_path):
   try:
     output = common.RunAndCheckOutput(cmd)
   except common.ExternalError as e:
-    raise ApexInfoError, \
+    raise ApexInfoError(
         'Failed to get APEX payload info for {}:\n{}'.format(
-            payload_path, e), sys.exc_info()[2]
+            payload_path, e))
 
   # Extract the Algorithm / Salt / Prop info from payload (i.e. an image signed
   # with avbtool). For example,