Expose advanced help in bin/omero import

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Refactor CLI import unit tests to define a setup_method

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Refactor omero.plugins.import module import (cf integration tests)

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Move CLI import help test as unit test

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Add unit tests for all help arguments

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Migrate TestImportDepth to the CLI import unit tests

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Do not assume help argument return zero codes

bin/omero import -h return a zero code (argparse) while the Java help
processes return non-zero codes

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Add unit test for test.fake import

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Merge pull request #2765 from sbesson/rebased/develop/import_advanced_help

Add advanced help to the bin/omero import command (rebased onto develop)