Eggtest: support --shared_part_list

Shared parts received from test node will be passed as
SLAPOS_TEST_SHARED_PART_LIST environment variable to egg tests.

This will be useful for SLAPOS-SR tests.
8 jobs for feat/testnode_shared_part in 0 seconds
Status Job ID Name Coverage
  External
passed SlapOS.Eggs.UnitTest-Jerome.Python2

00:13:19

passed SlapOS.Eggs.UnitTest-Jerome.Python3

00:50:23

failed SlapOS.Eggs.UnitTest-Jerome.Python2

01:03:53

passed SlapOS.Eggs.UnitTest-Jerome.Python2

passed SlapOS.Eggs.UnitTest-Jerome.Python2

00:52:37

passed SlapOS.Eggs.UnitTest-Jerome.Python2

00:17:23

passed SlapOS.Eggs.UnitTest-Jerome.Python2

00:13:52

passed SlapOS.Eggs.UnitTest-Jerome.Python3

01:33:02