Cert: Add InitiateConnectionForSecurity to PyL2cap

This is needed from the Security module's cert test component
called PySecurity.  It will need to allow for a cert device to
initiate a bond.  In order to create the bond we will need to establish
a link and follow some of the same logic in place in C++ and translate it
here.

From Security it will need to access PyL2cap in order to call InitiateConnectionForSecurity.

Bug: 162984360
Test: cert/run L2capTest:test_initiate_connection_for_security
Tag: #gd-refactor
Change-Id: I587a52be58217372fe1716319c1f4448dade1693