fix installation failure if pip is not installed yet

With "-e" flag, "$?" syntax does not work. If the line before "$?" exits
other than 0, the scripts stops at the line and never reach the next
line.

Closes-Bug: #1327918
Change-Id: I9de2392d972c8dbdb0df3ea4ce2e256fd9cb723c
Merge "fix installation failure if pip is not installed yet"