Run session creation in system context

In an effort to get rid of the periodic failing
tests with:
```
java.lang.IllegalArgumentException: No valid permissions available!
DUMMY permissions are not intended for copying. Make sure that you have
not passed omero.group=-1 for a save without context
```
make all calls to `SessionManagerImpl.createSession` run with an
explicit context for the system group.
Merge pull request #2450 from joshmoore/dummy-fix

Run session creation in system context
Update develop submodules

Repository: openmicroscopy/openmicroscopy
Already up-to-date.

Repository: openmicroscopy/bioformats
Updating f247b30..d4ec8df
Merged PRs (fast-forward):
  # PR 1083 rleigh-dundee 'make: Convert variables to ant properties'
  # PR 1075 hflynn 'Remove dead bitmap link (rebased onto develop)'
  # PR 1076 hflynn 'Adding CONTRIBUTING file to BF repo (rebased onto develop)'
  # PR 1073 rleigh-dundee 'docs: Delegate all sphinx Makefile targets to ant'

Repository: ome/scripts
Updating 31f89c4..7361669
Merged PRs (fast-forward):
  # PR 79 sbesson 'Travis fix (rebased onto develop)'

Repository: openmicroscopy/ome-documentation
Updating be161c6..84d1033
Merged PRs (fast-forward):
  # PR 776 sbesson 'Remove all references to CI jobs in the official documentation'
  # PR 772 rleigh-dundee 'make: Convert variables to ant properties'
  # PR 771 hflynn 'Adding pyramid generation data duplication warning to in-place import (rebased onto develop)'
  # PR 760 rleigh-dundee 'Make Ice 3.4 the minimum supported version'
  # PR 768 hflynn 'Rephrasing CONTRIBUTING re: branch for PRs (rebased onto develop)'
  # PR 769 hflynn 'Making API doc links point at release version (rebased onto develop)'
  # PR 766 rleigh-dundee 'ant: Default all properties and handle empty vars in conf.py'
  # PR 758 hflynn 'Adding API doc links to OMERO docs front page (rebased onto develop)'
  # PR 759 hflynn 'ticket 10030 fix - contributing file for docs repo (rebased onto develop)'
  # PR 761 rleigh-dundee 'Delegate all Makefile targets to ant'

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