fix docker & ccache

[casperdcl]

• fix docker builds: fix fix docker builds #195, partially revert Travis changes for OSX and docker #209
  • ensure docker builds do not fail silently: fixes Travis should turn red when unit tests fail #194
  • upgrade docker images to ubuntu 18.04 (from 16.04)
    • fix boost
• use ACE, ITK in docker builds
• fix ccache in docker
• use newer ccache syntax for normal travis builds

depends on #212 -> #213

[casperdcl]

ok now getting (https://api.travis-ci.org/v3/job/499919417/log.txt):

test 3
    Start 3: Gadgetron_TESTS
...
3: 1: [  FAILED  ] 2 tests, listed below:
3: 1: [  FAILED  ] hoNDArray_blas_Cplx/0.nrm2Test, where TypeParam = std::complex<float>
3: 1: [  FAILED  ] hoNDArray_blas_Cplx/2.nrm2Test, where TypeParam = Gadgetron::complext<float>

[KrisThielemans]

hmmm. strange as 18.04 is their reference system.

I'll try to see in a VM if I can reproduce this. Only possibly reason that I see is the addition of the two CBLAS lines when building Gadgetron? sorry. not really what you want to have to fix.

[casperdcl]

Turns out libatlas-base-dev was required (#195 (comment)) even though their List of Dependencies does not mention it.

In the end I just used https://github.com/gadgetron/gadgetron/blob/b03e500/docker/base/ubuntu_1804/Dockerfile#L8-L10

[KrisThielemans]

could presumably later use docker/build_essential-ubuntu.sh in Travis (and of course VM etc etc), except that we might need to pass location as not everyone will be able to write in /opt