plugins/sources/pip.py: Accomodate characters '-','.','_' for packages

See merge request !914

Fixes: 825963b5 ("element: Make "--sysroot" take a bare directory")

element.py: Pass bare_directory also to SandboxRemote()

See merge request !928

Issue happens with sourceware.org server.

Fixes #742

Use less fetchers in overnight build to work-around limitations from servers.

Closes #742

See merge request !929

richardmaw-codethink authored Nov 05, 2018 and richardmaw-codethink committed Nov 05, 2018

"_frontend/app.py: Set correct element-path in interactive bst-init"
added a dependency on the tmp_path test fixture, which was added by 3.8.

dev-requirements: Update pytest dependency to 3.8

See merge request !930

There are arguments for and against using onerror - see issue #735
for details.