The PETSc version of vsnprintf(). Converts a PETSc format string into a standard C format string and then puts all the function arguments into a string using the format statement.
str - location to put result
len - the amount of space in str
format - the PETSc format string
fullLength - the amount of space in str actually used.
this function may be called from an error handler, if an error occurs when it is called by the error handler than likely a recursion will occur and possible crash.