reduce CI time of high_level_api tests

* slimming test_parallel_executor_seresnet.py

* Add an option to enable the cache of expected kernel in train phase.
test=develop

* Change the default value of cache_expected_kernel to true.

test=develop

test=develop

* fix too long unittest
recommit
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* add fake_reader.py
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Move dygraph api to root

add attr scale. test=develop

disable seqpool concat pass by default saving CI time

* bug-fix, test=develop

* tweak code, test=develop

test=develop

list of fixed ops:
lookup_table_op
space_to_depth_op
squared_l2_distance_op
squared_l2_norm_op
teacher_student_sigmoid_loss_op
tree_conv_op
warpctc_op

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reduce hasAttr elapsed time in RunImpl

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* make less batch of tests to fit ci

* test=develop, invoke ci

add some comments back

* test fuse all_reduce

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Cache the chosen kernel of operators

test=develop

* Try to enable the runtime_context_cache pass in train phase.

* Put the append of runtime_context_cache pass ahead of multi_dev passes.
test=develop

reduce all analyzer_test ci elasped time

comment np.array(x.get_tensor()) in imperaitve mode to avoid OOM.

fix dataset bug

test=develop