qa/tasks: fix SyntaxWarning for invalid escape sequences in vstart_runner.py

qa/tasks: fix SyntaxWarning for invalid escape sequences in vstart_runner.py

Convert regex patterns to raw strings to fix the following warnings:
- Line 673: SyntaxWarning: invalid escape sequence '\s'
- Line 798: SyntaxWarning: invalid escape sequence '\.'
- Line 905: SyntaxWarning: invalid escape sequence '\['
- Line 911: SyntaxWarning: invalid escape sequence '\s'
- Line 1072: SyntaxWarning: invalid escape sequence '\['
- Line 1185: SyntaxWarning: invalid escape sequence '\('

All regex strings now use the r"..." prefix to treat backslashes
literally, which is the standard practice for regular expressions
in Python.

Signed-off-by: Kefu Chai <k.chai@proxmox.com>