* travis: remove verbose from Swarm race tests

By removing -v our output will be cleaner, but the Travis job still
won't be terminated - due to 'no output for 10 minutes' - as keepalive
.sh produces a log line every 5 minutes.

* travis: extend Swarm race detection to p2p subpackages

As p2p/protocols, p2p/simulations and p2p/testing packages mostly
belong to the Swarm team.

* travis, build: switch to NDK 19b, fix gomobile builds

* travis, build: move NDK into its final bundle location

* travis: disable Android build on PRs once again

* build: use sftp for launchpad uploads

* .travis.yml: configure sftp export

* build: update CI docs

* travis, appveyor: bump to Go 1.11.4

* internal/build: revert comment changes

* travis: exclude non-test jobs for PRs

We don't usually look at these builders and not starting them
removes ~15min of build time.

* build: don't run vet before tests

Recent versions of Go run vet during 'go test' and we have
a dedicated lint job.

* build: use -timeout 5m for tests

Tests sometimes hang on Travis. CI runs are aborted after 10min with no
output. Adding the timeout means we get to see the stack trace for
timeouts.

This commit is meant to allow ecosystem projects such as ethersphere
to minimize CI build times by specifying an environment variable with
the packages to run tests on.

If the environment variable isn't defined the build script will test
all packages so this shouldn't affect the main go-ethereum repository.

This is supposed to fix the FTP upload issue according to
travis-ci/travis-ci#9391.

* crypto/bn256: full switchover to cloudflare's code

* crypto/bn256: only use cloudflare for optimized architectures

* crypto/bn256: upstream fallback for non-optimized code

* .travis, build: drop support for Go 1.8 (need type aliases)

* crypto/bn256/cloudflare: enable curve mul lattice optimization

* travis.yml: work around Go 1.9.4 issue

* travis: workaround the workaround

This works around travis-ci/travis-ci#8703.

This avoids setting CC for the go run invocation, which fails on go1.10.

Also remove installation steps for fuse and golang.org/x/tools/cmd/cover 
because they're not required anymore.

* build: [finishes #15372] implements generalized linter and travis job

* .travis, build: minor polishes, disable deadcode