Adding "ck test package" to test all packages

[gfursin]

CC @ens-lg4 , @psyhtest .

Since we use official and often non-permanent URLs to download and install packages (websites, GitHub, etc), we sometimes have issues that URLs change or even disappear. There are two solutions:

• long-term: we should add a permanent storage (what we already do in some cases via cKnowledge.org) for packages. I've also heard that spack developers plan to add such a permanent repository for different packages and maybe we will be able to use it. However, some packages such as Java do not allow distribution of their packages outside Oracle website and often change location - that is a big issue.

• current: we should add "ck test package:*" command to test all packages - this should be done not at the time of commit (i.e. via Travis), but using our own machine with lots of space. In such case, it can delete all env entries and installations, and attempt to install all packages from scratch. There is a trick to make it non-interactive if there are multiple versions of subdependencies or possible compilers - we need to think about that. Maybe we can create "test" scenarios for each package to reduce testing combinations for now ...

However, I think such functionality is of high priority now to keep all packages and workflows working!