Use ZooContext instead of environment variable for orca_eager_mode (#2468)
Use ZooContext instead of environment variable for orca_eager_mode (#2468)

* maintain orca eager mode flag

* fix
yangw1234/BigDL,yangw1234/BigDL,yangw1234/BigDL,intel-analytics/BigDL,intel-analytics/BigDL,yangw1234/BigDL,intel-analytics/BigDL,intel-analytics/BigDL