[v1.x]Fix Nightly CI

[access2rohit]

Description

Update v1.x Nightly CI CPU/GPU image to ubuntu 18
Update Rat check image to ubuntu 18

Checklist

Essentials

• PR's title starts with a category (e.g. [BUGFIX], [MODEL], [TUTORIAL], [FEATURE], [DOC], etc)
• Changes are complete (i.e. I finished coding on this PR)
• All changes have test coverage
• Code is well-documented

Changes

Running Will post results once complete.

[mxnet-bot]

Hey @access2rohit , Thanks for submitting the PR
All tests are already queued to run once. If tests fail, you can trigger one or more tests again with the following commands:

• To trigger all jobs: @mxnet-bot run ci [all]
• To trigger specific jobs: @mxnet-bot run ci [job1, job2]

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CI supported jobs: [clang, sanity, centos-cpu, windows-cpu, unix-cpu, website, centos-gpu, windows-gpu, unix-gpu, edge, miscellaneous]

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Note:
Only following 3 categories can trigger CI :PR Author, MXNet Committer, Jenkins Admin.
All CI tests must pass before the PR can be merged.

[mseth10]

LGTM

[waytrue17]

LGTM!

[access2rohit]

Local run succeded:

$ ci/build.py --docker-registry 021742426385.dkr.ecr.us-west-2.amazonaws.com/mxnet-ci --platform ubuntu_nightly_cpu --docker-build-retries 3 --shm-size 500m /work/runtime_functions.sh build_ubuntu_cpu_large_tensor
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[442/445] Linking CXX static library libmxnet.a
[443/445] Linking CXX executable im2rec
[444/445] Linking CXX shared library libmxnet.so
[445/445] Linking CXX executable tests/mxnet_unit_tests

[mseth10]

LGTM