ShellCommand: De-virtualize environment()

Provide instead a protected setter, used in VcsCommand c'tor.

Remove a forceCLocale arg from setProcessEnvironment() method,
as it is used only in VcsCommand context when
ShellCommand::ForceCLocale flag was set. Move setting
C locale env directly to the shell command, just before
the command is executed, so that we are sure the flag
was already set.

Modify env directly in VcsCommand c'tor with regards to
SSH_ASKPASS variable.

Change-Id: Icff555ade4984368f7ce79f762d1bb5d3614076a
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/vcsbase/vcscommand.h

@@ -36,9 +36,6 @@ class VcsCommand : public Utils::ShellCommand
 {
     Q_OBJECT
 
-protected:
-    Utils::Environment environment() const override;
-
 private:
     VcsCommand(const Utils::FilePath &defaultWorkingDirectory,
                const Utils::Environment &environment);