Standardise global state in create_mets_v2

The `create_mets_v2` client script uses a bunch of global state for
things like counters and file IDs.  The original implementation could
rely on these globals being reset between runs (by virtue of running
the script in a new subprocess each time) but, after the batching
changes, this is no longer the case.

To make things more manageable, we pull all of this global stuff into
a single top-level object which gets replaced at the beginning of each
job run.  Where other modules call the functions of create_mets_v2,
they reset the global state as appropriate as well.

A secondary piece of shared state is the
`sharedVariablesAcrossModules` module, used by `create_mets_v2` and a
handful of other scripts.  Handling for this needed to be updated for
the batching changes in a small number of places.

Fixes archivematica/Issues#43 and archivematica/Issues#42

src/MCPClient/lib/clientScripts/archivematicaCreateMETSReingest.py

@@ -300,13 +300,14 @@ def add_new_files(job, mets, sip_uuid, sip_dir):
         return mets
 
     # Set global counters so getAMDSec will work
-    createmets2.globalAmdSecCounter = int(
-        mets.tree.xpath('count(mets:amdSec)', namespaces=ns.NSMAP))
-    createmets2.globalTechMDCounter = int(
-        mets.tree.xpath('count(mets:amdSec/mets:techMD)', namespaces=ns.NSMAP))
-    createmets2.globalDigiprovMDCounter = int(
-        mets.tree.xpath('count(mets:amdSec/mets:digiprovMD)',
-                        namespaces=ns.NSMAP))
+    createmets2.initGlobalState(
+        globalAmdSecCounter=int(mets.tree.xpath('count(mets:amdSec)',
+                                                namespaces=ns.NSMAP)),
+        globalTechMDCounter=int(mets.tree.xpath('count(mets:amdSec/mets:techMD)',
+                                                namespaces=ns.NSMAP)),
+        globalDigiprovMDCounter=int(mets.tree.xpath('count(mets:amdSec/mets:digiprovMD)',
+                                    namespaces=ns.NSMAP))
+    )
 
     objects_fsentry = mets.get_file(label='objects', type='Directory')
 

src/MCPClient/lib/clientScripts/create_aic_mets.py

@@ -160,5 +160,6 @@ def call(jobs):
     with transaction.atomic():
         for job in jobs:
             with job.JobContext():
+                create_mets_v2.initGlobalState()
                 args = parser.parse_args(job.qrgs[1:])
                 create_aic_mets(args.aic_uuid, args.aic_dir, job)