FIX: Set DistributedPluginBase.refidx type correctly

[effigies]

Summary

In 39c4ee3, we had

     def _generate_dependency_list(self, graph):
         """ Generates a dependency list for a list of graphs.
         """
         self.procs = graph.nodes()
-        self.depidx = nx.adj_matrix(graph).__array__()
-        self.refidx = deepcopy(self.depidx>0)
-        self.refidx.dtype = np.int8
+        self.depidx = ssp.lil_matrix(nx.adj_matrix(graph).__array__())
+        self.refidx = deepcopy(self.depidx)
+        self.refidx.astype = np.int
         self.proc_done    = np.zeros(len(self.procs), dtype=bool)
         self.proc_pending = np.zeros(len(self.procs), dtype=bool)

This looks like a typo, that should have been self.refidx = deepcopy(self.depidx).astype(np.int) or similar.

In this PR, I simply use self.depidx.astype(int). scipy.sparse.lil_matrix.astype copies by default.

Found while removing a deprecated call to np.int.

I also remove a guard for networkx versions that were old in 2012: b908b84

[codecov]

Codecov Report

Merging #3340 (f250f5c) into master (d02750a) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #3340   +/-   ##
=======================================
  Coverage   65.01%   65.01%           
=======================================
  Files         302      302           
  Lines       40035    40031    -4     
  Branches     5291     5291           
=======================================
- Hits        26029    26027    -2     
+ Misses      12935    12933    -2     
  Partials     1071     1071           

Flag	Coverage Δ
unittests	64.79% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
nipype/pipeline/plugins/base.py	58.17% <100.00%> (+0.08%)	⬆️

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[effigies]

Didn't break things. Will merge before a 1.6.1 release, unless I see an objection.