Perform agent startup-attach before bind

We were performing agent startup-attach during bind but this was too
late for some agents, as it occurred after Context was created. Change
implementation to make this occur prior to bind.

Test: atest CtsJvmtiAttachingHostTestCases
Bug: 142010970
Change-Id: I5f75e8b3c508116762b7863d9b47251d0e808ea9