Add integration test for sessions login diagnostics message

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Add quiet attribute to omero.cli.Context to suppress self.err()

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Expose -q (quiet mode) in all plugins using configure_login

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Test login diagnostics with and without quiet mode

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Move -q arguments to add_login_arguments

- Remove -q argument from hql plugin to prevent conflicts
- Store -q argument as isquiet and use this variable in  omero.cli.Context

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Unify -q/--quiet login arguments with the hql plugin

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Fix double space in argument help

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Delegate the isquiet check for self.err() to the CLI plugins
Merge pull request #2667 from sbesson/12291_cli_quiet

Add a quiet option to CLI commands