test: Robustify cleanup of dmidecode in TestSystemInfo.testHardwareInfo
test: Robustify cleanup of dmidecode in TestSystemInfo.testHardwareInfo

Sometimes the text file is still busy, retry until it works.

cockpit-project/cockpit,martinpitt/cockpit,mvollmer/cockpit,martinpitt/cockpit,mvollmer/cockpit,cockpit-project/cockpit,martinpitt/cockpit,martinpitt/cockpit,mvollmer/cockpit,mvollmer/cockpit,martinpitt/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,mvollmer/cockpit