Use full path sdkmanager for all android images

[webbertakken]

Changes

• Use full path sdkmanager to accept licenses
• Re-enables 2018.2 and below
• Closes Some additional environment variables #84

Pending

• Confirmation that 2018.2 and 2018.1 builds are indeed fixed by this

Checklist

• Read the contribution guide and accept the code of conduct
• Readme (updated or not needed)

[github-actions]

[mob-sakai]

2018.2 does not support C# 6.0, so the build script needs to be modified.
https://github.com/game-ci/docker/pull/90/checks?check_run_id=2017760557#step:14:1493

-----CompilerOutput:-stderr----------
Assets/Editor/Editor/Input/AndroidSettings.cs(11,58): error CS1644: Feature `out variable declaration' cannot be used because it is not part of the C# 6.0 language specification
Assets/Editor/Editor/Input/AndroidSettings.cs(13,58): error CS1644: Feature `out variable declaration' cannot be used because it is not part of the C# 6.0 language specification
Assets/Editor/Editor/Input/AndroidSettings.cs(15,58): error CS1644: Feature `out variable declaration' cannot be used because it is not part of the C# 6.0 language specification
Assets/Editor/Editor/Input/AndroidSettings.cs(17,58): error CS1644: Feature `out variable declaration' cannot be used because it is not part of the C# 6.0 language specification
Assets/Editor/Editor/Input/ArgumentsParser.cs(15,37): error CS1644: Feature `out variable declaration' cannot be used because it is not part of the C# 6.0 language specification
Assets/Editor/Editor/Input/ArgumentsParser.cs(17,60): error CS1644: Feature `out variable declaration' cannot be used because it is not part of the C# 6.0 language specification
Assets/Editor/Editor/Input/ArgumentsParser.cs(22,60): error CS1644: Feature `out variable declaration' cannot be used because it is not part of the C# 6.0 language specification
Assets/Editor/Editor/Input/ArgumentsParser.cs(31,64): error CS1644: Feature `out variable declaration' cannot be used because it is not part of the C# 6.0 language specification
Assets/Editor/Editor/Input/ArgumentsParser.cs(37,64): error CS1644: Feature `out variable declaration' cannot be used because it is not part of the C# 6.0 language specification
Assets/Editor/Editor/Versioning/Git.cs(109,82): error CS1644: Feature `out variable declaration' cannot be used because it is not part of the C# 6.0 language specification
Assets/Editor/Editor/Versioning/Git.cs(109,101): error CS1644: Feature `out variable declaration' cannot be used because it is not part of the C# 6.0 language specification

License activation fails in 2018.1.
https://github.com/game-ci/docker/pull/90/checks?check_run_id=2017760571#step:14:141

BTW, the test project was created in 2018.3, so it will not work properly in 2018.2 or earlier.

[webbertakken]

I removed the pre 2018.3 part, so this will support usage of java/sdkmanager outside of unity for all versions from 2018.3 and up.