b4 tool installation: Fallback to pip based installation

lisa/tools/b4.py

@@ -1,7 +1,8 @@
 import pathlib
 import re
 from lisa.executable import Tool
-from lisa.operating_system import Posix
+from lisa.operating_system import Debian
+from lisa.tools.python import Pip
 from lisa.util import get_matched_str
 
 
@@ -17,8 +18,12 @@ def can_install(self) -> bool:
         return True
 
     def _install(self) -> bool:
-        if isinstance(self.node.os, Posix):
+        if isinstance(self.node.os, Debian):
             self.node.os.install_packages("b4")
+        installed = self._check_exists()
+        if not installed:
+            pip = self.node.tools[Pip]
+            pip.install_packages("b4", install_to_user=True)
         return self._check_exists()
 
     def am(self, message_id: str, output_dir: pathlib.PurePath) -> pathlib.PurePath: