set BZR_HOME env var so bzr won't fail

Dependencies

• [2] JRVI4XTV tests: Use $(builddir) instead of `pwd`.
• [*] G2ZB6464 first test, not yet in buildprocess

Change contents

• edit in tests/Makefile.am at line 2
  [2.26]

  [2.26]
  + BZR_HOME="$(abs_builddir)/data" \