feat(install): Add automatic logs to install script (#312)

This change makes the install script create a new install log file, `sentry_install_log-<ISO_TIMESTAMP>.txt`, for each run and records all the output there for future reference.

.gitignore

@@ -33,6 +33,7 @@ var/
 # Installer logs
 pip-log.txt
 pip-delete-this-directory.txt
+sentry_install_log*.txt
 
 # Unit test / coverage reports
 htmlcov/