This PR makes use of go 1.13 error handling, wrapping errors and using
errors.Is to check a wrapped root-cause. It also removes the travis
builders for go 1.11 and go 1.12.

* travis, appveyor, build, Dockerfile: bump Go to 1.14.2

* travis, appveyor: force GO111MODULE=on for every build

* travis: remove debug traces

* travis: Add travis_wait to the test run

* travis: increase travis_wait time

* build: use golangci-lint

This changes build/ci.go to download and run golangci-lint instead
of gometalinter.

* core/state: fix unnecessary conversion

* p2p/simulations: fix lock copying (found by go vet)

* signer/core: fix unnecessary conversions

* crypto/ecies: remove unused function cmpPublic

* core/rawdb: remove unused function print

* core/state: remove unused function xTestFuzzCutter

* core/vm: disable TestWriteExpectedValues in a different way

* core/forkid: remove unused function checksum

* les: remove unused type proofsData

* cmd/utils: remove unused functions prefixedNames, prefixFor

* crypto/bn256: run goimports

* p2p/nat: fix goimports lint issue

* cmd/clef: avoid using unkeyed struct fields

* les: cancel context in testRequest

* rlp: delete unreachable code

* core: gofmt

* internal/build: simplify DownloadFile for Go 1.11 compatibility

* build: remove go test --short flag

* .travis.yml: disable build cache

* whisper/whisperv6: fix ineffectual assignment in TestWhisperIdentityManagement

* .golangci.yml: enable goconst and ineffassign linters

* build: print message when there are no lint issues

* internal/build: refactor download a bit

* travis: Enable ARM support

* Include fixes from 20039

* Add a trace to debug the invalid lookup issue

* Try increasing the timeout to see if the arm test passes

* Investigate the resolver issue

* Increase arm64 timeout for clique test

* increase timeout in tests for arm64

* Only test the failing tests

* Review feedback: don't export epsilon

* Remove investigation tricks+include fjl's feeback

* Revert the retry ahead of using the mock resolver

* Fix rebase errors

* build: bump PPAs to Go 1.13 (via longsleep), keep Trusty on 1.11

* travis, build, vendor: use own Go bundle for PPA builds

* travis, build, internal, vendor: smarter Go bundler, own untar

* build: updated ci-notes with new Go bundling, only make, don't test

* vendor: remove unused dependencies

These were used by swarm code, which has now migrated to its own repository.

* travis.yml: remove sudo requirement for test builders

These needed sudo to run FUSE tests for swarm.

* 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.