* Allow converting keras.layers.Sequential

* Use existing new_var function

* Only update expr when missing

* Add test

Adopt the "set -u" idiom from the docker scripts as a mechanism to
improve future robustness.

* Fix Relay ARM CPU spatial pack depthwise alter op layout issue.

* Update tune_relay_arm.py

A number of test scripts use the '|| exit 1' idiom.  This has two
issues, first process exit codes are defined to be in the range 0-255.
Second, more importantly, the idiom is fragile because it requires
that every possible failure point be explicitly coded.  This patch
removes the idiom in favour of "set -e" as used in the docker scripts
as a more robust mechanism to ensure that script failures are always
caught and propagated by default.

* Add dense schedules to __init__ for cpu

* Add documentation for topi::shape

* Add additional imports to topi CPU __init__.

* [Relay][Op] Add group conv2d dispatch to topi function

* Rerun tests

* decompile tf control flow

* Add docs

* remove import relay

* move tests under tensorflow frontend

* minor fix

* Fix error reporting for missing axis

* Update data_layout.cc

* improved `multiply_rewrite` for gluoncv_ssd quantization

* add a check to attach_simulated_quantize below to prevent quantizing lhs to INPUT if lhs_kind is INPUT;

The dict which is used to initilize OrderDict is not ordered, so
  metadata may not be at the end.

* Add ops in mxnet converter

* trigger ci

* [AlterLayout] NCHW upsampling

* [Relay][Pass] Fix Depthwise AlterLayout

* [Relay][Frontend][keras] added interpolation method of Upsampling2D.

* added testcase

* small fixes