Closes: #3761

The idea behind this change is to have 2x (and maybe later 3x, 4x, ...)
bucket for alpha and beta releases. See more details about the release
process in the documentation: [1].

[1]: https://tarantool.io/en/doc/2.0/dev_guide/release_management/

Main branch was renamed to master.
Update .travis.yml accordingly.

Replaced targets generation using a matrix expansion + exclusion list
with the explicit targets list. Gave meagingful names for targets.

Fixes #3673.

We made a mistake when tagging 1.7.5, which confused git describe.
Now we have added more tags and the hack with removal can be deleted.

- Remove old versions of Fedora and Ubuntu
- Add Fedora 26 and Fedora 27

Patch removes Ubuntu Precise from Travis's testing matrix,
since it uses really outdated GCC v.4.6.x.

Switched from ubuntu zesty to artful, since zesty is EOLed on 13Jan2018

Remove all non-LTS versions of Ubuntu.

PackageCloud doesn't support Ubuntu Artful yet.

Follow up e3d97f6d

Closes #2805

Travis images are broken by design.

Ubuntu Trusty on Travis is buggy.

Fixes #2752

Ubuntu Trusty on Travis is buggy.

Fixes #2752

git describe picks 1.7.5 as a closest tag on 1.8 branch.
Temporary remove 1.7.5 tag to fix 1.8.x packages.

* Switch to PackPack for packages
* Use `packagecloud` deployment for packages instead of travis.sh script
* Use `script` deployment for sources instead of travis.sh script
* Package all branches, but upload only 1.6/1.7
* Move all Travis CI script into the single Makefile

Rumprun is a toolchain to build unikernels based on NetBSD/Rump kernel.
Compiled images can be booted on KVM/XEN and even on "bare metal".

Unfortunally, Tarantool unikernels are still not fully functional due to
bugs in libeio and LuaJIT. However, now we have a simple way to check
cross-compilation for BSD/Rumpkernel and to bake unikernels from the code:

    OS=rumprun DIST=hw packpack
    qemu-system-x86_64 -enable-kvm -kernel build/tarantool-1.7.3.265.img

Make Travis CI green again!

Rawhide and Sid are bleeding edge technlogies.

Blobs and minified JS are prohibited by distributions.
Fixes packages on Debian Sid.

See #1939