Managesieve: Fix parsing config string on Windows

Managesieve: Fix parsing config string on Windows

Windows sscanf() does not understand the %ms format yet, so we
have to do the allocation of target buffer ourselves before
calling sscanf(), and copy the host string to config->host.

Also fix some off-by-one bugs in other sscanf() parameters - the
field width format modifier does not include trailing NUL byte,
which is added.