install.sh: setup workdir correctly on nonroot mode
install.sh: setup workdir correctly on nonroot mode

Specify correct workdir on nonroot mode, to set correct path of
data / commitlog / hints directories at once.

Fixes #5475

Signed-off-by: Takuya ASADA <4ebfb6f510af412d6e89fefa3ab96d9c8b5e3fff@scylladb.com>
Message-Id: <20191213012755.194145-1-4ebfb6f510af412d6e89fefa3ab96d9c8b5e3fff@scylladb.com>

scylladb/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla