Fixes #3697

The existing code and test case only covered the leader behavior. When
querying against non-leaders the error has an "rpc error: " prefix.

To provide consistency in HTTP error response I also strip the "rpc
error: " prefix for 403 responses as they offer no beneficial additional
information (and in theory disclose a tiny bit of data to unauthorized
users, but it would be a pretty weird bit of data to use in a malicious
way).

Fix detection of successful batch allocations

This PR restores older behavior of detecting successful batch
allocations (04d86ffd). This has the
side effect that we correctly filter desired status stop but not
successful batch allocations and create their replacements.

Add missing -group=cache to docs

Prevent absolute URLs in checks paths

Fixes #3699

Merges recent work from 0.8 branch

Make macos/osx builds optional in Travis

securing guide: small signal typo and argument consistency

Mentions min CPU limit change in backward incompatibilities section.

revert change to increase min. CPU resource value from 20 to 100

Add missing token option for nomad run command

Change 'CoreOS rkt' to just 'rkt'

In the commit 622d3ddb
"Fixed test and moved constants into standalone func" the minimum CPU
resource value for a job was increased from 100 to 20.

This can break the nomad setup for people that used lower CPU
values and are at the maximum MHz value of the available CPU on a
machine.
Change the minimum back to 20 MHz to ensure downwards compatibility.

CoreOS initiated the project but it is now under the CNCF banner and includes many contributors and core maintainers that are not at CoreOS.

Search endpoint forwarding

code review fixups; add changelog

Services should not require a port

Fixes #3673