Introduce FLASHFILE variable to start migrating boards to use it.
This is the file that will be used for flashing.
Boards do not currently use it but will migrated in upcoming PRs.
This introduces a new environment variable for a common directory
that holds all output of the build process, such as application or
package binaries. This would also allow to easily redirect output
to any other location, e.g. for out-of-source builds.
This makes doing 'scan-build-analyze' produce an error at execution if
WERROR=1.
When used from `scan-build` it will not procude an error to display the result
webpage.
This correctly defines a `scan-build-analyze` target that does not display the
result webpage.
`scan-build-view` has now been moved to a private target as should not
be used directly.
The handling of displaying the page on the host system and implementing
'scan-build-analyze' are now explicitely done with separate targets and
not double implemented target when in docker or on the host that were executed
twice with different implementations.
