systrace: handle user builds more gracefully
systrace: handle user builds more gracefully

This change adds an indication of which command line args require root to the
--help output.  It also defers opening the output file until after the trace
has actual started being dumped so that if atrace exits with an error the
output file is not truncated.

Bug: 6513400
Change-Id: Ifa0ed1d3d5eef891fee7d9109c2bb988b03c2e4d

Omegaphora/external_chromium-trace,xhteam/external-chromium-trace,xin3liang/platform_external_chromium-trace,Pankaj-Sakariya/android-source-browsing.platform--external--chromium-trace,ThangBK2009/android-source-browsing.platform--external--chromium-trace,Pankaj-Sakariya/android-source-browsing.platform--external--chromium-trace,bhargavkumar040/android-source-browsing.platform--external--chromium-trace,xhteam/external-chromium-trace,rcoscali/external-chromium-trace,xhteam/external-chromium-trace,SaleJumper/android-source-browsing.platform--external--chromium-trace,ThirdProject/android_external_chromium-trace,Omegaphora/external_chromium-trace,ThirdProject/android_external_chromium-trace,ganadist/chromium-trace,Omegaphora/external_chromium-trace,VanirAOSP/external_chromium-trace,android-ia/platform_external_chromium-trace,rcoscali/external-chromium-trace,rcoscali/external-chromium-trace,xin3liang/platform_external_chromium-trace,geekboxzone/lollipop_external_chromium-trace,android-ia/platform_external_chromium-trace,VanirAOSP/external_chromium-trace,ganadist/chromium-trace,VanirAOSP/external_chromium-trace,xin3liang/platform_external_chromium-trace,SaleJumper/android-source-browsing.platform--external--chromium-trace,CyanogenMod/android_external_chromium-trace,xin3liang/platform_external_chromium-trace,android-ia/platform_external_chromium-trace,rcoscali/external-chromium-trace,SaleJumper/android-source-browsing.platform--external--chromium-trace,SaleJumper/android-source-browsing.platform--external--chromium-trace,xin3liang/platform_external_chromium-trace,ganadist/chromium-trace,ganadist/chromium-trace,Pankaj-Sakariya/android-source-browsing.platform--external--chromium-trace,xhteam/external-chromium-trace,CyanogenMod/android_external_chromium-trace,geekboxzone/lollipop_external_chromium-trace,mer-tools/chromium-trace,Omegaphora/external_chromium-trace,bhargavkumar040/android-source-browsing.platform--external--chromium-trace,geekboxzone/lollipop_external_chromium-trace,CyanogenMod/android_external_chromium-trace,geekboxzone/lollipop_external_chromium-trace,CyanogenMod/android_external_chromium-trace,ThangBK2009/android-source-browsing.platform--external--chromium-trace,android-ia/platform_external_chromium-trace,ThangBK2009/android-source-browsing.platform--external--chromium-trace,ThirdProject/android_external_chromium-trace,mer-tools/chromium-trace,Pankaj-Sakariya/android-source-browsing.platform--external--chromium-trace,ThirdProject/android_external_chromium-trace,mer-tools/chromium-trace,bhargavkumar040/android-source-browsing.platform--external--chromium-trace,mer-tools/chromium-trace,bhargavkumar040/android-source-browsing.platform--external--chromium-trace,VanirAOSP/external_chromium-trace,ThangBK2009/android-source-browsing.platform--external--chromium-trace,VanirAOSP/external_chromium-trace,mer-tools/chromium-trace